Our biochemically oriented investigations of schistosomes, filariae, and mosquito vectors of filariae have revealed that certain peculiarities of their nucleic acid and folate metabolism are potentially exploitable for chemotherapy of schistosomiasis and filariasis or for mosquito vector control with appropriate antimetabolites. Four promising findings that emerged from our research will be more thoroughly probed to assess their potential for practical application or to serve as the basis for the development of innovative disease control technologies. These are: (1) the use of mammalian host red cells as delivery vehicles for antischistosomal drugs, taking advantage of the high rate of red cell ingestion by these trematodes; (2) the detection of increased dihydrofolate reductase activity in Brugia pahangi-infected Aedes aegypti, with preliminary evidence that inhibition of this mosquito enzyme at a critical time during the course of infection was associated with the recovery of fewer infective filarial larvae. Further study of this and other biochemical aspects of the mosquito-filaria relationship might eventually lead to the development of chemical agents which could cause othewise susceptible mosquitoes to become unsuitable hosts for filarial parasites; (3) the finding that adult filariae (Litomosoides carinii, Dirofilaria immitis, Dipetalonema viteae, and Onchocerca volvulus) possess relatively high dihydrofolate reductase activity, thus presenting an inviting target for attack by selectively toxic antifols; (4) the finding that two thiocyanatouridine derivatives exhibited both schistosomicidal and macrofilaricidal activity in vitro at concentrations in the 0.01 mM range. These are the first pyrimidine analogs to show significant anthelmintic activity.